GMPhotography wrote:
Fred and my copies of the Ultron matched the same focusing spots both with filter on and off so I ordered a TAP for myself after he told me if his settings and confirmed infinity. I should have a bunch of shots to post when I get back to Phoenix. Having a lot of fun with it

I hope it works for you Guy!

Something else I noticed is that with the PCX the lens focuses closer. (A good 2 inches closer)
If using a helicoid adapter (like TAP) and focusing very close (0.2m), I found that I need to stop the lens down to at least f/2.5 to maintain the same resolution level. (compared to the lens MFD)

Can't complain about this because the lens wasn't designed to focus closer than 0.5m...

Fred, if by longer you mean that the focal length increases then no, itís actually the opposite. When you add a positive diopter element to any lens, the focal of the combo becomes shorter. Itís a basic law of optics. The simplified formula is : F3 = F1*F2/(F1+F2). Where F3 is the final length, F1 is the focal of the original lens and F2 is the focal of the PCX filter.
In this case : F3 = 35*5000/(35+5000) = 34.76
Thatís why youíre able to focus nearer when you use this PCX on your CV 35/1.7. The focal goes from the original 35mm to 34.76mm. To practical effects, itís like adding a 0.24mm. tiny extension tube. Therefore you can focus nearer than with the Ďnakedí lens. Of course that means also that, in order to reach infinity, you need to shorten 0.24mm. the length of the adapter or remove internal shims from the lens.

artur5 wrote:
Fred, if by longer you mean that the focal length increases then no, itís actually the opposite. When you add a positive diopter element to any lens, the focal of the combo becomes shorter. Itís a basic law of optics. The simplified formula is : F3 = F1*F2/(F1+F2). Where F3 is the final length, F1 is the focal of the original lens and F2 is the focal of the PCX filter.
In this case : F3 = 35*5000/(35+5000) = 34.76
Thatís why youíre able to focus nearer when you use this PCX on your CV 35/1.7. The focal goes from the original 35mm to 34.76mm. To practical effects, itís like adding a 0.24mm. tiny extension tube. Therefore you can focus nearer than with the Ďnakedí lens. Of course that means also that, in order to reach infinity, you need to shorten 0.24mm. the length of the adapter or remove internal shims from the lens....Show more →

Math is math and we can't argue with it.

In practical terms though, I didn't see any different in FL at infinity (with and without the PCX). If there is a difference, it's minimal and definitely not wider.

The CV 35/1.7 Ultron is a bit longer than my Loxia 35 at infinity to begin with.

Here are two crops showing the extreme edges at infinity. The left image is without the PCX and the right with it. I don't see a noticeable change in FL at this distance.

Yea I just noticed it when testing the FE side by side that the CV is longer but Fred did mention the FE is really 33mm which I did not know . Well going to head out and shoot the heck out of it today. Look forward to the TAP and the A9 firmware update when I get home. Iím shooting with the KF adapter right now. Interesting my Llawo 15 and CV 35 both at infinity are right at the start of the infinity mark. Truth be told with this Llawo 15 Iím questioning my 12-24 now. I would not mind buying back the Firin 20mm and a cheap 24-70 for PR work. But Iím hard pressed to do it since I have a great 12-24 on hand. I love shooting this 15 by a truckload. Im just very tactical when it comes to lenses. I Ike the feel of MF lenses

Here is a super high quality () iPhone shot showing the CV 35/1.7 Ultron + PCX on a TAP:

46-55mm ring (To avoid any vignetting when using additional filters), blank 55 (Tiffen brand, UV glass removed), 5m PCX and El-pro3 retaining ring. I used a rubber O-ring to keep the front-lens perfectly centered. It looks like a protection filter on the lens.

Fred, Guy, Bastian and many others who tested this, thank you! The results look great. Quick question. How did you remove the UV glass from the Tiffen ring? Just break it? Does the filter stay in place using the o ring or the retaining clip or both? Do I need any special tools to do this mod?

46-55mm ring (To avoid any vignetting when using additional filters), blank 55 (Tiffen brand, UV glass removed), 5m PCX and El-pro3 retaining ring. I used a rubber O-ring to keep the front-lens perfectly centered. It looks like a protection filter on the lens.

Iíll break it unless there is a retaining ring. Only tool you may need is a spanner wrench. 12 dollars on Amazon but only if your dealing with a retaining ring to hold filter down. My 55-52 step down holds it in place so no need

I have a CV 35 1.7 and am interested in getting the PCX filter given Fred's pictures showing the clear improvement.

I'm a bit confused though about the other items -- step up ring, retaining ring, etc. I assume the step up is needed because the PCX doesn't come in the right size for the lens? Why are the other items needed?

If someone has figured out exactly what is needed to be ordered, I'd be grateful!